Power operated rotary knives are widely used in meat processing facilities for meat cutting and trimming operations. Such power operated rotary knives typically include a handle assembly including a head member extending from the handle assembly, an annular blade housing coupled to the head member via a clamp assembly, and an annular rotary blade supported for rotation by the blade housing. The annular rotary blade of a conventional power operated rotary knife is rotated by a drive mechanism including a flexible drive shaft which extends through an opening in the handle assembly and engages a pinion gear supported in a distal portion of the handle assembly head member. The flexible drive shaft includes a stationary outer sheath and a rotatable interior drive shaft which is driven by a pneumatic or electric motor. Gear teeth of the pinion gear engage mating gear teeth formed on an upper surface of an annular body of the annular rotary blade. A blade section of the rotary blade extends downwardly from the annular body. Upon rotation of the pinion gear by the flexible drive shaft, the annular rotary blade rotates within the blade housing at a high RPM, on the order of 1,500-2,000 RPMs. Conventional power operated rotary knives are disclosed in U.S. Pat. No. 6,354,949 to Baris et al., U.S. Pat. No. 6,751,872 to Whited et al., U.S. Pat. No. 6,769,184 to Whited, and U.S. Pat. No. 6,978,548 to Whited et al., all of which are assigned to the assignee of the present invention and all of which are incorporated herein in their respective entireties by reference.
Depending upon the application, power operated rotary knives are offered in various sizes. Size may be measured in terms of an outer diameter of the annular rotary blade. Typical annular rotary blade may vary in size from, for example, as 1.4 inches to over 7 inches. For a given annular blade rotational speed, e.g., 2000 RPM, it is clear that the linear velocity of an outer surface of the blade bearing against the blade housing increases with increasing blade diameter. As such, problems of wear on the blade bearing surface and vibration of the blade as it rotates within the blade housing are accentuated in power operated rotary knives with large blade diameters. As used herein, rotary knife blades with outer diameters of approximately 5 inches or greater are considered large diameter blades, such blades being particularly prone to the problems discussed herein.
The blade housings of large diameter rotary knives typically include a split blade housing for blade replacement while the blade housing remains attached to the handle assembly head member. The clamping assembly is loosened on one side of the split of the split blade housing thereby allowing one end of the blade housing adjacent the split to be moved away from the other end of the blade housing. Relative movement of the one end of the blade housing away from the other end expands the blade housing diameter and allows removal of a blade and insertion of a new blade, while the other end of the blade housing remains attached to the head member. Upon insertion of a new blade, the blade housing is returned to its unexpanded state and the loosened side of the clamping assembly is tightened to secure the blade housing in place.
Unfortunately, properly returning and securing the blade housing to its unexpanded state tends to be a trial and error procedure, especially for new, untrained operators of a power operated rotary knife. If the blade housing diameter is returned to a diameter that is too small for the blade, the blade will tend to stick or potentially lock up in the blade housing. If the blade housing diameter is returned to a diameter that is too large for the blade, the blade will not be properly supported in the blade housing and will tend to vibrate.
A problem with larger diameter blades involves wear on the radial outermost surface of the blade. In conventional large diameter power operated rotary knives, the radially outermost surface of the blade corresponding to the drive gear region of the blade, that is, the upper region of the blade where the plurality of gear teeth are formed, functions as a bearing surface. As such, the blade housing contacts and bears against the radial outer surface of the drive gear region of the blade. This causes the radially outer surface of the blade drive gear region to wear down as the blade rotates in the blade housing, thereby reducing the effective outer diameter of the blade.
Reducing the outer diameter of the blade in the blade drive gear region causes problems in terms of increased vibration. That is, as the blade outer diameter decreases, the blade becomes looser within the blade housing and hence is prone to vibration within the housing at high rotational speeds. Increased vibration makes the knife more difficult to operate and increases operator fatigue. The operator will either look for another knife or be forced to attempt to adjust the diameter of the blade housing to a smaller diameter to match the decreased blade diameter. Such adjustments or attempted adjustments of the blade housing diameter on the part of the operator decrease operator productivity and increase operator dissatisfaction with the knife, both of which are undesirable results.
In FIG. 13, a section view of a portion of a prior art large diameter power operated rotary knife is shown. The prior art blade 500 and blade housing 502 are shown to schematically illustrate the blade—blade housing bearing structure 504. The prior art bearing structure 504 includes a first, cylindrical bearing surface 506 of the blade housing 502, which bears against a mating cylindrical bearing surface 508 of the blade 500, a second, frustoconical bearing surface 510 of the blade housing 502 which bears against a mating frustoconical bearing surface 512 of the blade 500, and a third, horizontally oriented annular bearing surface 514 of the blade housing 502 which bears against a mating horizontal, annular bearing surface 516 of the blade 500. As can be seen, the first cylindrical bearing surface 508 of the blade 500 includes a radial outer surface of a drive gear section 518 of the blade and the third horizontal annular bearing surface 516 of the blade includes an upper surface of the drive gear section of the blade.
Not all of the mating bearing surfaces of the blade—blade housing are in contact at any given time because there are necessarily running clearances between the blade 500 and the blade housing 502 which allow the blade to rotate relatively freely within the blade housing. These running clearances cause the blade 500 to act somewhat akin to a teeter-totter within the blade housing 502, that is, as one region of the blade is pivoted or moved upwardly within the blade housing during a cutting or trimming operation, the diametrically opposite portion of the blade (180° away) is pivoted or moved downwardly within the blade housing. Accordingly, the mating bearing surfaces in contact at a specific location of the blade—blade housing interface will change and, at any given time, will be determined by the forces applied during use of the rotary knife.
For example, if, when viewed from the perspective of the operator, the right side of the blade 500 is being used for cutting or trimming meat, i.e., the region labeled T in FIG. 2, the blade edge 520 in the region T (the loaded side of the blade) will transmit a force vector along the blade generally in the direction labeled F in FIG. 13. This will cause the mating blade housing—blade bearing surfaces 506, 508 and the mating blade housing—blade bearing surfaces 514, 516 to be moved into contact to restrain the blade 500 within the blade housing 502, i.e., the blade housing bearing surfaces 514, 506 restrain upward and radial outward movement of the blade with respect to the blade housing, respectively. At the same time, the diametrically opposite region of the blade 500, the region labeled O in FIG. 2, that is, the unloaded side of the blade, will experience a force vector in a direction F′ which is generally perpendicular to the direction F shown in FIG. 13, that is, bearing against the blade housing bearing surface 510. The blade 500 will tend to move generally downwardly and radially inwardly within the blade housing 502, thus, the blade housing—blade bearing surfaces 510, 512 will be in contact in to restrain movement of the blade within the housing in the region O. At that same time, in the region O, the blade housing—blade bearing surfaces 514, 516 and 506, 508 may not be in contact because of the teeter-tooter pivoting of the blade within the housing.
A problem with the prior art bearing structure shown in FIG. 13 is that the cylindrical blade bearing surface 508 is comprised of a plurality of gear teeth, that is, the radial surface 508 has gaps between each pair of adjacent gear teeth, for example, adjacent gear teeth 522, 524 have a gap 526 between them. Because of the gaps in the cylindrical blade bearing surface 508 and the small axial height of that surface on the order of 0.034 inch, the area of the bearing surface 508 is small. Given the large loading forces applied to the cylindrical surface 508 during cutting and trimming operations, in the prior art design, the radial outer surface of the prior art blade 500 will wear rapidly during use.
As the radial outer surface 508 is the largest outer diameter of the blade 500, the result of such wear of the radial outer surface 508 is that the blade 500 outer diameter will decrease and the blade will tend to vibrate in the blade housing 502. As the radial outer surface 508 wears, the blade 500 becomes looser and looser within the blade housing 502. Increasing vibration will result in greater operator fatigue and lower productivity. An inexperienced operator may simply accept the increased vibration as a necessary part of using a power operated knife and reduce productivity by cutting slower, turning the knife off, taking additional time between cuts, etc.
An experienced operator may recognize that a potential solution to the problem of increased vibration is to adjust, that is, reduce the blade housing diameter to account for the decreased outer diameter of the blade. As described above, adjustment of the blade housing diameter involves loosening the clamping screw 65, using a screwdriver or other tool to leverage the slot 76 against the head member 24 to adjust blade housing diameter, and then tightening the clamping screw. There are numerous problems with this approach. First, it is a trial and error technique that requires the operator to find a suitable blade housing diameter. For example, if the blade housing diameter is made too small, the blade may lock up in the housing. Second, even if the operator is successful in adjusting the blade housing to an acceptable diameter, valuable working time has been lost in the adjustment process. Finally, since wear of the radial outer surface 508 of the blade 500 is ongoing, the adjustment is only a temporary fix as further wear occurs.
What is needed is a blade—blade housing bearing structure for large diameter power operated rotary knives that results in less wear in the radial outermost surface of the blade, that is, less wear in the radial outer surface of the blade drive gear region. What is also needed is a blade—blade housing bearing structure for large diameter power operated rotary knives that results in less vibration of the knife as the knife is used. What is also needed is a blade—blade housing bearing structure that is less sensitive to blade housing diameter adjustment errors and/or requires less blade housing diameter adjustments.